Special Senses (Nalley)
Breakdown the receptor responses to stimuli.
What are the four types of information transmitted?
Modality – type of stimulus (eg light, vibration)
Determined by Where sensory signals ends in brain
Location – determined by receptive field and its size
Intensity – how strong or weak a signal is
Influences how many sensory neurons firing
Duration – how long stimulus lasts
Sensory receptors have a sensory adaptation mechanism – prolonged stimulus slows neuron firing over time
What are the differences between tonic and phasic receptors?
Tonic Receptors
Adapt slowly and generate signals more steadily
Proprioceptors & pain receptors
Phasic Receptors
Generate burst of action potentials when first stimulated
Reduce or stop signaling, even if stimulus continues
Ex. Smell, hair movement, cutaneous pressure & vibration
What are the five modality types of receptors?
Thermoreceptors – heat & cold
Photoreceptors – light
Nociceptors – pain receptors
Chemoreceptors – chemicals (odors, tastes, body fluid composition)
Mechanorecptors – physical deformation (vibration, touch, pressure, stretch, tension)
Hearing & balance, skin, viscera & joints
How are receptors organized by stimulus origin?
Exteroceptors – external stimuli
Vision, hearing, taste, smell, cutaneous sensations (touch, heat, cold, pain)
Interoceptors – internal stimuli
Stretch, pressure, visceral pain, nausea
Proprioceptors – position & movement
Muscles, tendons, joint capsules
What are the broad differences between unencapsulated and encapsulated nerve
ending receptors?
Unencapsulated Nerve Ending Receptors – Dendrites with no connective
tissue wrapping
1. Free nerve endings – provide temperature and pain
 Warm, cold & nocieceptors
 Bare dendrites with no special cell/tissue association
 Most abundant in skin & mucous membranes
2. Tactile discs (tonic receptors for light touch)
 Flattened nerve endings that terminate next to specialized tactile
cells in epidermis basal layer
 Compression of skin releases a chemical from tactile cell that
excites associated nerve
3. Hair receptors
 Dendrites around hair follicle, respond to movement
 Adapt quickly
Encapsulated Nerve Ending Receptors Nerve fibers wrapped in glial cells or connective tissue.
Most are mechanoreceptors (touch, pressure, stretch)
Connective tissue enhances:
 Sensitivity of nerve fiber
 Selectiveness for modality
1. Tactile corpuscles (phasic receptors for light touch & texture)
 2 or 3 nerve fibers in fluid-filled capsule of Schwann cells
 Linked to skin dermal papillae
 Concentrated in sensitive hairless areas (fingertips, palms, eyelids)
2. End bulbs
 Functionally similar to tactile corpuscles
 Mucous membranes (lip, tongue, conjunctiva)
 Connective tissue sheath around sensory nerve fiber
3. Bulbous corpuscles (tonic receptors – heavy touch, pressure, stretching,
deformation, joint movements)
 Perception of shape
 Dermis, subcutaneous tissue & joint capsules
 Flattened capsules containing few nerve fibers
4. Lamellar Corpuscles (phasic receptors – vibration)
 Bone periosteum, joint capsules, pancreas & other viscera, deep dermis
 Single dendrite encapsulated by concentric cell layers
5. Muscle spindles (proprioception, stretch)
 Skeletal muscle near tendon
6. Tendon Organs (proprioception, stretch)
 Tendons
Operationalize the projection pathways for:
Taste - What is the pathway(s) from tongue to cerebrum?
1. Stimuli Received
 Anterior 2/3 tongue - Facial Nerve (CN VII)
 Posterior 1/3 tongue – Glossopharyngeal Nerve (CN IX)
 Palate, pharynx epiglottis – Vagus Nerve (CN X)
2. All taste fibers go to medulla oblongata
3. Neurons relay signals to two (2) destinations
 Hypothalamus & amygdala activate autonomic reflexes (salivation, gagging, vomiting)
 Thalamus relays signals to cerebrum
4. Signals relayed to cerebrum integrate with eyes & nose info
 Flavor
 Palatability
What are the features of the tongue that communicate stimuli information
and how do they differ from each other?
Filiform papillae – no taste buds
 Rough, small, most abundant
 Food texture
Foliate papillae
 Parallel ridges on side of tongue where most chewing
occurs & flavor chemicals released
 Taste buds degenerate by age 2 or 3
Fungiform papillae – 3 taste buds
 Widely distributed, food texture
Vallate papillae – contains half of all taste buds
 Arranged in V at back of tongue
 Surrounded by deep circular trench, taste buds located on
papilla wall
 7-12 total
Smell – What is the pathway from nasal cavity to
cerebrum/brainstem?
1. Stimuli received – olfactory fibers pass through ethmoid to
olfactory bulbs
2. Synapse with dendrites of mitral & tufted cells
3. Olfactory axons meet dendrites in glomeruli
 Each glomerulus is dedicated to type of odor
4. Tufted & mitral cells carry output from glomeruli – forming olfactory tracts
5. Olfactory tracts end in temporal lobe
6. Signals then travel to cerebrum & brainstem:
 Cerebrum – ID odors
 Brainstem – links smell & strong memories, emotional responses, visceral reactions
What is the function of each cell type along this path?
Olfactory cortex also sends fibers to olfactory bulbs called granule cells
Granule cells can inhibit mitral & tufted cells
Hearing/Balance – What are the pathway differences for
hearing and equilibrium?
Hearing
1. Sound waves  Tympanic Membrane  Ossicles Oval
Window Inner ear Fluid:
 Pushes on basilar membrane
 Pressure relieved by round window
2. Basilar membrane vibrates:
 Movement pushes hair cells closer to tectorial
membrane
 Bending hairs open connected ion channel & depolarize it
3. Hair cells release neurotransmitter; excites cochlear nerve & signal is
transmitted to brain
Equilibrium
1. Three semicircular ducts: anterior, posterior & lateral
 Filled with endolymph & detects rotation
 Each opens into utricle and has dilated sac (ampulla)
2. Crista ampullaris – mound of hair & supporting cells, cupula
3. Cupula – gelantinous cap extending over hair cells
4. Hair cells in macula sacculi, macula utriculi, & semicircular ducts synapse with vestibular nerve
 Merges with cochlear nerve  CN VIII
5. CN VIII fibers to brainstem (pons & medulla oblongata)
What functions are performed at the five terminal targets for the equilibrium pathway?
Process signals of position & movement & relay to five targets:
1. Cerebellum – integrates head & eye movements, muscle tone, posture
2. CNs III, IV & VI – vestibulo-ocular reflex – allows to keep vision fixed when toward object.
3. Brainstem – adjusts breathing/circulation to posture changes
4. Spinal cord – signal muscles to maintain trunk & limbs
5. Cerebrum – conscious awareness of position & movement
What reflexes are involved in the hearing pathway?
1. Sensory fibers located at hair cells bases
2. Axons lead away from cochlea as cochlear nerve joins vestibular nerve  CN VIII
3. Signals head to Pons
 Cochlear tuning
 CN V3 & VII for tympanic reflex
4. Signal to Midbrain
 Cerebrum & primary auditory cortex
 Neck muscles for auditory reflex
Sight – What is the pathway from orbit to occipital lobe?
1. Optic nerves leave each orbit via optic canal
2. Converge to form Optic Chiasm
 Half of fibers cross over to opposite side of
brain
3. Fibers continue as Optic Tracts
4. Most Optic Tract axons to Thalamus
 To visual cortex of occipital lobe
 Conscious visual sensation
What reflexes are regulated in the midbrain?
Few optic nerves fibers to midbrain
 Visual reflexes of extrinsic eye muscles
 Photopupillary & accommodation reflexes
Identify & Describe anatomy of:
Ear: Describe the major features of the outer, middle, and inner ear.
Outer Ear
 Funnel conducting vibrations to tympanic membrane
 Pinna – elastic cartilage except earlobe (adipose tissue)
 Auricle – Whorls & recesses that direct sound to auditory canal
 External acoustic meatus – passage leading thru temporal bone to tympanic membrane
 Ceruminous/sebaceous gland secretions mix with skin cells & form cerumen (earwax)
Middle Ear
 Located in tympanic cavity (temporal bone)
 Continuous with mastoidal air cells in
mastoid process
 Filled with air via auditory tube (connects to
nasopharynx)
 Aerates, drains middle ear
 Auditory ossicles connect tympanic
membrane to inner ear: Malleus, Incus,
Stapes
 Stapes base is held in oval window
(opening to inner ear)
Inner Ear
 Bony labyrinth
 Lined by membranous labyrinth
 Perilymph - btw bony & membranous labyrinths
 Endolymph – within membranous labyrinth
 Vestibule – equilibrium organs
 Cochlea – hearing organs, has three fluid-filled
chambers
 Scala vestibuli – Superior chamber; oval
window to apex
 Scala tympani – Inferior chamber; apex
to round window
o Filled with perilymph &
communicate via narrow channel at cochlea apex
 Cochlear duct – middle chamber; separated by two endolymph-filled membranes (vestibular &
basilar)
How are sound waves transformed into neural signals? What is the pathway and what structures are involved and
what are their functions?
1. Sound waves  Tympanic Membrane  Ossicles Oval Window Inner ear Fluid:
 Pushes on basilar membrane
2. Basilar membrane vibrates which converts the vibrations into nerve impulses
 Movement pushes hair cells closer to tectorial membrane
 Bending hairs open connected ion channel & depolarize it
3. Hair cells release neurotransmitter; excites cochlear nerve & signal is transmitted to brain
How are changes in position, as well as speed, detected? What structures communicate this information?
In the cochlea, there are three fluid-filled chambers.
 Scala vestibuli is the superior chamber
 Scala tympani is the inferior chamber
 Chochlear duct is the middle chamber
 Separated by two endolymph filled membranes (Vestibular & Basilar).
o vestibular apparatus has three semicircular ducts & two chambers.
 Two chambers are the Saccule & Utricle
 Each have hair and supporting cells called macula. These hair cells are embedded in
gelatinous otolithic membrane filled with otoliths.
 Macula utriculi, located in the Utricle give horizontal orientation &
detects head tilt.
 Macula sacculi located in the Saccule gives vertical orientation &
detects acceleration & deceleration.
Eye: Describe the major features of the orbit and eye.
Eyebrows – enhance facial expression/nonverbal communication, protect eyes from glare/ perspiration
Eyelids – block foreign objects, prevent visual stimui, moisten eye, sweep debris
 Separated by palpebral fissure
 Meet at medial & lateral commissures
Tarsal plate – supportive fibrous thickening along eyelid
margin (lacrimal punctum)
Orbital fat – surrounds eye; cushions, permits movement,
protects vessels
What is the pathway for tears from gland to nasal cavity?
Tear pathway after Lacrimal gland
Lacrimal punctum lacrimal canaliculus  lacrimal sac 
nasolacrimal duct  nasal cavity
What is the autonomic innervations and responses for the lacrimal gland?
Parasympathetics
 CN VII  CN V1  Gland
Sympathetics
 Sympathetic Chain  Cervical sympathetic Ganglion  Internal Carotid A.  CN VII  CN V1  Gland
What are the three main tunics of the eye and what are their components?
Tunica fibrosa – outer layer with two regions; sclera & cornea
 Sclera – protective covering, dense
collagenous connective tissue
 Perforated by vessels & nerves
 Extrinsic muscle attachment
 Cornea – transparent covered by
stratified squamous epithelium anteriorly
& simple squamous epithelium
posteriorly
 Epithelia pump prevents
overhydrating, swelling, losing
transparency
Tunica vasculosa – middle layer with three
regions
 Choroid – vascular; pigmented layer
behind retina
 Ciliary body – muscular ring around lens, supports iris & lens
 Secretes aqueous humor
 Iris – adjustable diaphragm that controls pupil size
Tunica interna
 Retina
 Optic nerve (CN II)
What are the optical components of the eye? Transparent elements – admit & bend light focus images:
Aqueous humor – serous fluid secreted by ciliary body
 Reabsorbed by scleral venous sinus
Lens – flattened, tightly compressed, transparent fibers
 Suspended by suspensory ligament
Vitreous body – transparent jelly
What are the neural components?
Optic Nerve CN II
Retina – cup-shaped outgrowth of brain
 Thin, transparent membrane attached at 2 points
1. Optic disc – where optic nerve leaves eye
 Blood vessels enter/exit
 No receptor cells (blind spot)
2. Ora serrata – anterior margin of eye
 Macula lutea – posteror wall directly behind lens
 Fovea centralis – retina nerve fibers converge
here, finely detailed images
 Consists of 3 cell layers
 Photoreceptor cells - absorb light & generate a
chemical or electrical signal
 Rods & Cones synapse with
dendrites of bipolar cells, then
synapse with ganglion cells.
 Ganglion cells – largest neurons
of retina, axons form optic nerve
(CN II)
What are the differences between rods and
cones?
Rods & Cones – produce visual images
 Rods – night vision & shades of gray
(monochromatic) vision

Cones – day vision & color (trichromatic) vision
What is the autonomic innervation and responses for the eye? 
Parasympathetics (accommodation, pupil constriction):
 CN III  CN V1  lens & iris
Sympathetics (pupil dilation; open eyelids):
 Sympathetic Chain Cervical Sympathetic Ganglion Internal Carotid A. CN V1 Iris CN III 
eyelid